SEQUENCE CHARACTERIZATION AND EXPRESSION ANALYSIS OF THE FOXO GENE FAMILY IN MEGALOBRAMA AMBLYCEPHALA

FoxO (Forkhead box O) proteins belong to the members of the forkhead family and play important roles in life cycle regulation and the oxidative stress response. In order to study roles of FoxO family in fish, in this study, the coding sequences of 7 foxO genes, foxO1a/b, foxO3a/b, foxO4 and foxO6a/b in Megalobrama amblycephala were obtained through PCR amplification and omics sequencing, and were 1965, 1892, 1929, 1959, 1878, 1803 and 2157 bp in length respectively. SMART domain analysis showed that M. amblycephala FoxO proteins belonged to the typical FoxO family with conserved Forkhead (FH), FOXO_KIX_bdg and FOXO-TAD domains. Phylogenetic tree analysis showed that FoxO amino acid sequences of M. amblycephala had higher similarity with the homologous genes of other Cyprus fishes. Based on qPCR analysis, the mRNAs of 7 foxO genes were detected in all 9 tissues of M. amblycephala, but also showed expression changes in different tissues, which foxO4 was mainly expressed in the blood, foxO6a was mainly expressed in the liver, and foxO6b was mainly expressed in the brain. During the early development of M. amblycephala embryos, the expression patterns of foxO1a/foxO1b, foxO3a/foxO3b, and foxO6a/foxO6b were similar. However, foxO4 expression levels were low at early development stages except body segment appearance stage, late-eyeball pigment stage, the somatic node formation stage and 10 days post fertilization. After acute hypoxia treatment, the expression levels of 7 foxO genes in most of the detected tissues were significantly up-regulated, especially in the muscle. Meanwhile, JASPAR analysis showed that all foxO family genes contained Hif-1 α binding sites, and the foxO1b promoter was verified by Dual Lucifase reporter system, and found to be regulated by Hif-1α. These results suggested that foxO gene may play an important role in hypoxic stress of M. amblycephala through Hif-1α mediated pathway.